The Intricate Challenge within the Cellular Realm
The Analogy of a Delicate Task
How can one puncture the yolk inside an eggshell without breaking the shell? This might seem like a scenario from a science – fiction work. However, some scientists are making living cells perform highly delicate tasks similar to this in the laboratory. If we compare a cell to an egg, a team led by the University of California, San Diego, aims to develop a tool that can easily pierce the cell nucleus without harming the rest of the cell. From the perspective of an organism’s design, the nuclear membrane exists to keep the contents of the nucleus separate from the rest of the cell. On the surface of the nuclear membrane, complexes of dozens of proteins form gateways that control the entry and exit of substances. These nuclear pore complexes are like portals to the nucleus, allowing only specific molecules to pass through, safeguarding our genetic code.
The Barrier in Biomedical Research
This is the result of evolution and the basis of our body’s organization. But for biomedical scientists, it’s like a “curse”. The “channels” of the nucleus tend to reject the candidate drugs they want to deliver into the nucleus. However, some therapies, especially gene therapy, require direct delivery of genetic material into the nucleus for precise treatment. It can be said that delivering drugs across the nuclear membrane has always been a huge challenge. Scientists have been constantly attempting to develop new tools to break through this barrier and allow drugs to enter the nucleus. Currently, the methods to enter the nucleus usually involve using a fine needle to physically pierce the cell and the nucleus. But these methods are invasive and are likely to damage the rest of the cell, only suitable for small – scale applications.
The Innovation of Nanomaterials
Nanotopography: A Promising Solution
Recently, this research team reported in the journal Advanced Functional Materials that a series of nanopillars they created can pierce the nucleus inside the cell without destroying the cell’s outer membrane. Zeinab Jahed, an associate professor in the Department of Chemistry and Nanoengineering at the University of California, San Diego, and the corresponding author of this study, has long been interested in a type of material called “nanotopography”. These materials are bionic structures designed by simulating natural structures, including nanopillars, nanoneedles, and nanowires. They can bypass biological barriers such as the plasma membrane by simulating the spike proteins of viruses. These properties enable these materials to be used in intracellular sensing and drug – delivery platforms, and some of them are already in clinical trials.
The Interaction between Nanomaterials and the Nucleus
There has been much research on the interaction between nanotopography and the cytoplasmic membrane. For example, the geometry of nanotopography can induce cytoplasmic membrane remodeling or increase endocytosis. However, our understanding of the interaction between these materials and other organelles is still limited. Recent studies have found that the nanomorphology can deform organelles such as the nucleus, leading to nuclear membrane remodeling. Other researchers have also confirmed that nanopillars can cause nanoscale dents in the nuclei of living cells, and the depth of these dents is related to the size of the nanopillars, the spacing between them, and the softness of the nucleus. These studies all indicate that nanomaterials with different morphologies can directly affect the morphology and even the function of cell structures such as the nucleus.
The Experiment and Observation
Jahed and colleagues focused on engineered nanotopographic structures for disrupting the nuclear membrane, especially nanopillars. They had previously studied methods of manufacturing nanopillars to change the geometry of these nanostructures, including size and spacing. Briefly, they used lithography processes, as well as dry and wet etching. Under a scanning electron microscope, the researchers saw that these nanopillars really looked like tiny pillars. Then, they placed various types of cells, including cardiomyocytes, skin cells, and fibroblasts, on top of these pillars to observe what would happen inside the cells. In fact, based on previous research, they originally expected that these nanostructures might induce nanoscale curvature in the plasma membrane and the nuclear membrane, or that these membranes would exhibit positive and negative curvatures. However, the results showed that only the nucleus wrapped itself around the nanopillars, causing the nuclear membrane to bend and resulting in tiny openings in the nuclear membrane. Meanwhile, the cell’s outer membrane seemed to be undamaged.
Testing the Integrity of the Cell Membrane
To further test this, they labeled the cells with Ku – 80, a factor that can indicate nuclear membrane rupture (a protein usually located in the nucleus of most cell types). The results showed that in several cells placed on the cell pillars, Ku – 80 leaked from the nucleus to the cytoplasm, indicating that the nuclear membrane was ruptured, causing the contents of the nucleus to leak out. At the same time, these indicator factors only appeared inside the cell and did not escape outside the cell, further proving that the cytoplasmic membrane was intact and only the nuclear membrane was pierced. It is worth mentioning that in another experimental platform without cell pillars, no leakage of Ku – 80 from the nucleus to the cytoplasm was observed. Interestingly, the researchers also observed the diffusion process from the molecular cytoplasm to the nucleus in the cells located on the cell pillars. These results suggest that the interaction between the cells and the nanotopographic structures can induce the nuclear membrane to open without other external stimuli and further promote the bidirectional movement of molecules between the cytoplasm and the nucleus.
The Temporariness of the Openings and Future Prospects
The Self – repair of the Nuclear Membrane
Subsequently, Jahed and colleagues wondered whether these openings were temporary or permanent. So, they performed live – cell imaging on the labeled cells and observed that the nuclear membrane would repair itself within about one and a half hours after rupture. In other words, the self – repair mechanism of the nuclear membrane might be activated during this period after being punctured. Moreover, as long as the cells were removed from the nanopillars, the nuclear membrane would repair itself.
The Significance and Unanswered Questions
The researchers were excited about these results because it means that they can use some nano – arrays to selectively create tiny gaps in the nuclear membrane to allow substances to directly enter the nucleus while keeping the rest of the cell intact. More importantly, these gaps are self – reparable. However, there are still some unresolved issues in their minds. For example, during the brief opening of the nuclear membrane, there may be uncontrolled molecular exchange between the cytoplasm and the nucleus. Will this affect other active cellular processes? Additionally, if used for treatment in the future, will nanomaterials with different shapes of nanotopography trigger unwanted host immune responses? Next, they are continuing to investigate the mechanism behind this effect to enable safer and more effective delivery of genetic material into the nucleus in the future.
